Techniques (pattern-forming techniques) in which a fine pattern is formed on top of a substrate, and a lower layer beneath that pattern is then fabricated by conducting etching with this pattern as a mask are widely used in the semiconductor industry for IC fabrication and the like, and are attracting considerable attention.
These types of fine patterns are typically formed from an organic material, and are formed, for example, using a lithography method or a nanoimprint method or the like. For example, in the case of a lithography method, a process is conducted in which a resist film formed from a resist composition containing a base component such as a resin is formed on top of a support such as a substrate, the resist film is subjected to selective exposure using radiation such as light or an electron beam, through a mask in which a predetermined pattern has been formed (a mask pattern), and a developing treatment is then conducted, thereby forming a resist pattern of predetermined shape in the resist film. Resist compositions in which the exposed portions change to become soluble in the developing solution are termed positive compositions, whereas resist compositions in which the exposed portions change to become insoluble in the developing solution are termed negative compositions.
Then, using this resist pattern as a mask, a semiconductor device or the like is produced by conducting a step in which the substrate is processed by etching.
In recent years, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization. Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays semiconductor device mass production using KrF excimer lasers and ArF excimer lasers has already commenced, and for example, lithography using ArF excimer lasers has enabled pattern formation with resolution at the 45 nm level. Furthermore, in order to further improve the resolution, research is also being conducted into lithography techniques that use exposure light sources having a wavelength shorter than these excimer lasers, such as F2 excimer lasers, electron beams, EUV (extreme ultraviolet radiation), and X rays.
The resist composition requires lithography properties such as a high level of sensitivity to these types of exposure sources, and a high resolution capable of reproducing patterns of minute dimensions. As a resist composition which satisfies these requirements, a chemically amplified resist composition is used, which includes a base component that exhibits changed alkali solubility under the action of acid, and an acid generator that generates acid upon exposure (for example, see Patent Document 1). For example, a positive chemically amplified resist typically contains, as a base component, a resin which exhibits increased alkali solubility under the action of acid, and during formation of a resist pattern, when acid is generated from the acid generator upon exposure, the exposed portions of the resist become alkali-soluble.
As a technique for further improving the resolution, a lithography method called liquid immersion lithography (hereafter, frequently referred to as “immersion exposure”) is known in which exposure (immersion exposure) is conducted in a state where the region between the objective lens of the exposure apparatus and the sample is filled with a solvent (an immersion medium) that has a larger refractive index than the refractive index of air (see, for example, Non-Patent Document 1).
According to this type of immersion exposure, it is considered that higher resolutions equivalent to those obtained using a shorter wavelength light source or a larger NA (numerical aperture) lens can be achieved using the same exposure light source wavelength, with no lowering of the depth of focus. Furthermore, immersion exposure can be conducted using existing exposure apparatus. As a result, it is expected that immersion exposure will enable the formation of resist patterns of higher resolution and superior depth of focus at lower costs. Accordingly, in the production of semiconductor devices, which requires enormous capital investment, immersion exposure is attracting considerable attention as a method that offers significant potential to the semiconductor industry, both in terms of cost and in terms of lithography properties such as resolution.
Immersion lithography is effective in forming patterns having various shapes. Further, immersion exposure is expected to be capable of being used in combination with currently studied super-resolution techniques, such as phase shift methods and modified illumination methods. Currently, as the immersion exposure technique, techniques using an ArF excimer laser as an exposure source are being the most actively studied. Further, water is mainly being investigated as the immersion medium.
Recently, a new lithography technique called the double patterning method has been proposed, in which a resist pattern is formed by conducting patterning two or more times (see, for example, Non-Patent Documents 2 and 3).
According to this double patterning method, it is thought that by forming a first resist pattern on a support using a first resist composition, and subsequently conducting additional patterning using a second resist composition formed on top of the support having the first resist pattern formed thereon, a resist pattern can be formed that has a higher resolution than a resist pattern formed using only a single patterning step.
[Patent Reference 1]
Japanese Unexamined Patent Application, First Publication No. 2003-241385
[Non-Patent Document 1]
Proceedings of SPIE, vol. 5754, pp. 119 to 128 (2005)
[Non-Patent Document 2]
Proceedings of SPIE, vol. 5256, pp. 985 to 994 (2003)
[Non-Patent Document 3]
Proceedings of SPIE, vol. 6153, pp. 1 to 19 (2006)